Add Baltic Ruby 2026 (#1098)

Author: marcoroth

_data/conferences.yml

@@ -3229,3 +3229,13 @@
   twitter: rubyconf
   date_precision: year
   mastodon: https://ruby.social/@rubyconf
+
+- name: Baltic Ruby 2026
+  location: Hamburg, Germany
+  start_date: 2026-12-31 # TODO: update once dates are confirmed
+  end_date: 2026-12-31 # TODO: update once dates are confirmed
+  date_precision: year
+  url: https://balticruby.org
+  twitter: balticruby
+  mastodon: https://ruby.social/@balticruby
+  announced_on: 2025-06-14